My Wife and I are running into the same issue with data usage, starting 2 months ago our usage jumped way up we have a 8 gig plan and never came close to using it all and now I've had to buy 2 gigs just to make it too the end of the cycle.
But the OP has no issue. They are using very little data. The OP just didn’t understand that data used during the day, is posted on the online account later. Read my reply and understand how checks work is much like how data is deducted from your allowance.
If you’re running over, it’s a problem with you and your phone, not the service provider.
Start tracking what apps and services are using more data.
Just an FYI, phones and apps are designed to make it easy for the user. That takes data. The more user-friendly a device is, the more data it is going to consume. Applications and services are more sophisticated, so they will use more and more data. And we haven’t arrived at 5g yet.